The state of the art relating to ultrasonic detectors operating by acoustic transmission through the liquid to be detected may be illustrated for example by the following patent documents:
Patent application GB 2 177 510 A PA1 German patent application DE 31 49 909 A1 PA1 U.S. Pat. Nos. 4,958,518; 4,787,240; 4,535,628; 4,432,231; 4,063,457.
The ultrasonic detectors described in DE 31 49 909 A1, U.S. Pat. Nos. 4,787,240 and 4,063,457 notably comprise elastic elements which are inserted between the transducers and their support and thus constitute an acoustic insulation.
Another type of liquid detector may moreover be mentioned which operates by ultrasonic propagation within a solid detecting body arranged in contact with the liquid to be detected. Detectors of this type are described for example in the patent applications FR 2 617 965 A1; FR 2 628 527 A1 and EP 0 372 700 A1.
Known ultrasonic detectors such as those cited above nevertheless require a more or less complicated structure, generally do not ensure control of their operation and have important limitations with regard to their respective fields of application.